An interesting notion. I’m going to once again take this from a Tumblr perspective, just because I think that’s a useful way of analyzing concepts to reach non-LIS people and it’s a fun exercise.
Some people on Tumblr, like me, will tag the ofness of a post in meticulous detail. (See my earlier post.) Who it’s of, if they’re in anything, fictional characters, seasons of programs, etcetera. Some people on Tumblr do this really interesting thing called tag meta, where in the section allotted for tagging ofness they write sprawling analysis of or thoughts related to the post and what they perceive as its aboutness. This is difficult because since they’re thoughts, not just keywords, they’re not really searchable, but it’s not uncommon to see someone reblogging a post with the last person’s tag meta copied on. (This is considered more graceful than adding analysis in the body of the post, generally.) I personally can’t do this because my OCD shines in my tagging system and its searchability (although I do have some subjective tags (“girlcrushes” and “boycrushes,” for example, because a picture that’s of Adrianne Palicki isn’t inherently about girlcrushes but boy howdy, for me it is) but I find it very interesting.
And my overall point here is that aboutness is, as has been said, more difficult to categorize and search but definitely can add value.